Humeral rotating burr guide

ABSTRACT

A bone cutting assembly. The bone cutting assembly includes a guide pin having a distal tip that may be securely inserted into a bone to define a cutting axis and a housing having a cam surface and features which allow the housing to be temporarily secured to the bone. The bone cutting assembly further includes a burr mounting arm which can be fitted on to the guide pin so that it can swing around the cutting axis and also translate up and down the guide pin. The burr mounting arm is configured to act against the cam surface as it is swung around the guide pin, so that the arm is caused to move up or down relative to the guide pin by the action of the cam surface.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of U.S. patent application Ser. No.13/348902 which was a divisional of U.S. patent application Ser. No.12/062952, entitled “HUMERAL ROTATING BURR GUIDE”, each of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to the field of orthopaedics,and more particularly, to an instrument for use in arthroplasty.

BACKGROUND OF THE INVENTION

Patients who suffer from the pain and immobility caused byosteoarthritis and rheumatoid arthritis have an option of jointreplacement surgery. Joint replacement surgery is quite common andenables many individuals to function properly when it would not beotherwise possible to do so. Artificial joints are usually comprised ofmetal, ceramic and/or plastic components that are fixed to existingbone.

One type of joint replacement surgery is shoulder arthroplasty. Duringshoulder arthroplasty, the humeral head must be resected to allow forthe insertion of a humeral stem into the intramedullary canal of thehumerus. The proximal end of the humerus includes the humeral head,which articulates with the glenoid cavity of the shoulder in a ball andsocket fashion. The humeral head is nearly hemispherical in form.

The prostheses typically used for shoulder arthroplasty include a stemportion designed to extend into the intramedullary canal of the humerusand a head portion designed to replace the humeral head. The headportion of the prosthesis extends angularly from the stem portion. Theresection of the natural humeral head must be made so that the angle ofthe cut corresponds to the angle between the stem and head portions ofthe prosthesis. In addition, the rotation of the cut varies to adjust tobone wear or capsulor looseness.

There are eight essential variables relating to humeral arthroplasty.These include: the diameter of curvature of the prosthesis; thepercentage of the sphere with this diameter that will be used asprosthetic articular surface; the superior/inferior position of thearticular surface relative to the humerus; the anterior/posteriorposition of the articular surface relative to the humerus; themedial/lateral articular aspect of the articular surface with respect tothe humerus; the anterior/posterior angulation (flexion/extension) ofthe articular surface relative to the prosthesis; the medial/lateralangulation (varus/valgus) of the prosthesis relative to the humerus;and, the rotational alignment of the prosthetic head with respect to thehumeral axis. The goal of prosthetic arthroplasty is to duplicate thenormal orientation of the humeral articular surface as well as itsdiameter of curvature and percentage of the sphere.

Many orthopaedic companies currently provide anatomically variableprosthesis with stems that facilitate adjusting the prosthesis to moreaccurately reflect the anatomy of the individual. For anatomicallyvariable prostheses, most surgical techniques call for a “freehand” cutof the humeral head. Others have rudimentary guides that facilitate aplanar cut but only allow for anterior/posterior (version) ormedial/lateral adjustment of the cutting plane.

When the humeral head resection is made free hand, the elbow of thepatient is flexed to 90° with the patient's forearm aimed at the midlineof the operating surgeon's trunk. The humerus is externally rotated toprovide the recommended degree of retrotorsion in relation to the axisof elbow motion. The resection is directed away from the surgeon,allowing the surgeon to reproduce the desired retrotorsion in the bonecut. A trial prosthesis may also be placed along the proximal humeralshaft as a guide for the proper inclination of the resection. Thepossibility for error exists with this free hand approach. Inaccurateresection can result in an ill-fitting prosthesis which may causecomplications for the patient and may eventually require replacement ofthe prosthetic device.

Also, when implanting a proximal humeral resurfacing implant with anextended articulation surface, removal of part or all of the humeralgreater tubercle is needed. This removal should allow for proper fittingand fixation of the implant and the extended articulation surface to theresurfaced humeral head and requires cutting in two planes. However,current cutting guides only allow for the cutting of the humeral greatertubercle in one plane at a time. Therefore, the surgeon would need toperform at least two cutting steps (and possibly use two differenttools) to properly prepare the humerus. There is a need for a cuttingguide that allows for a surgeon to be able to properly remove thehumeral greater tubercle in a single step.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, a cutting guidefor removal of bone during arthroplasty is provided. The cutting guideincludes a housing having a three-dimensional guide path as well as anarm coupled to the housing. The arm extends through the guide path andincludes a burr. As the arm is slid along the path, the burrsimultaneously cuts in two planes.

According to another embodiment of the present invention, a method forresecting a portion of a bone in arthroplasty is provided. The methodincludes providing a housing having a three-dimensional guide path. Anarm is placed in the housing, such that the arm is movable along thethree-dimensional guide path. The arm is coupled to the burr. The methodalso includes simultaneously resecting a portion of the bone in aplurality of planes with the burr.

According to yet another embodiment of the present invention, a cuttingguide for cutting a form of a head of a bone during arthroplasty isprovided. The cutting guide includes a housing adapted to be placed onthe head of the bone and an arm rotatably coupled to the housing. A burris coupled to the arm such that the burr is adapted to cut the from ofthe bone as the arm rotates about the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of a humeral cutting guide on a humerus;

FIG. 2 is a perspective view of the humeral cutting guide of FIG. 1;

FIG. 3 is a perspective view of a portion of FIG. 2;

FIG. 3A is a partially see-through view of a portion of the humeralcutting guide of FIG. 1;

FIG. 4A is a medial-lateral view of a resurfaced humeral head;

FIG. 4B is a lateral-medial view of a resurfaced humeral head;

FIG. 5 is a flow chart describing the operation of the humeral cuttingguide;

FIG. 6 is perspective view of an alternative embodiment of the presentinvention; and

FIG. 7 is an exploded view of the embodiment shown in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention and the advantages thereof are bestunderstood by referring to the following descriptions and drawings,wherein like numerals are used for like and corresponding parts of thedrawings.

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and described in the following written specification. It isunderstood that no limitation to the scope of the invention is therebyintended. It is further understood that the present invention includesany alterations and modifications to the illustrated embodiments andincludes further applications of the principles of the invention aswould normally occur to one skilled in the art to which this inventionpertains.

Referring now to FIGS. 1 and 2, a cutting guide 10 is provided thatallows for the cutting of a humeral head 12. The cutting guide 10 isused to remove a portion of the humeral head 12 to allow for theplacement of an implant (not shown). The cutting guide 10 includes ahousing 14. The housing 14 includes a three-dimensional guide path, suchas a slanted parabolic slot 16 for coupling to a burr 18. The slot 16extends longitudinally and laterally. The slot 16 defines the path thatthe burr 18 will cut. The multi-directional nature of the slot 16enables the burr 18 to move both in the proximal/distal plane and alsothe medial/lateral plane—thereby allowing for a multiplanar cut.

An arm 20 extends through the slot 16 and includes a burr-attachment endand a quick-connect end. The burr-attachment end is coupled to the burr18. The arm 20 is held in place in the slot 16 by an adjustable cylinder22. The arm 20 includes a burr restraint portion 24 that is used to holdthe burr 18 on its path. The adjustable cylinder 22 allows the surgeonto adjust the distance between the burr 18 and the housing 14, whichwill be described in more detail in reference to FIG. 3 below. Thequick-connect end 20 b of the arm 20 allows the surgeon to hold the burrwith one hand while holding a drill portion with the other hand.

The adjustable cylinder 22 includes an opening 26 that extendslongitudinally through the adjustable cylinder 22. The opening 26 isadapted to receive a guide pin 28. As shown in FIG. 1, the guide pin 28extends through opening 26 and a post 29 of the housing 14 into ahumerus 30 for holding the cutting guide 10 in place relative to thehumeral head 12.

The housing 14 also includes a pair of pin holes 31 a, 31 b on the sidesto align the housing anteriorly and posteriorly on the humeral head 12.Pins 32 a, 32 b fit through the pin holes 31 a, 31 b to further affixthe housing 14 to the humeral head 12. The pins 32 a, 32 b prevent thecutting guide 10 from sliding around on the humeral head 12.

Turning now to FIG. 3, a perspective view of the arm 20 is shown. Anelongated slot 33 extends through the arm 20. The elongated slot 33 isdimensioned so as to receive the guide pin 28. The arm 20 also includesa plurality of notches 34 that are adapted to correspond with anadjustable pin (not shown). In the embodiment shown in FIG. 3A, thenotches 34 extend around the arm 20 and engage a movable ridge 36 on theinside of the adjustable cylinder 22 (FIG. 3A). The ridge 36 coupleswith one of the notches 34, locking the arm 20 in a particular locationrelative to the housing 14. A button 38 is included on the top of theadjustable cylinder 22. As best shown in FIG. 3A, when the button 38 ispressed, the ridge 36 disengages the notch 34 so the user can slide thearm 20. In some embodiments of the present invention, the arm 20 mayinclude markings to aid the surgeon in measuring the distance betweenthe cylinder 22 and the burr 18, which will adjust the radius of the cutarea.

In an alternative embodiment, the cylinder 22 may include a notch andthe arm 20 may include ridges. In other embodiments, other knownreleasable locking mechanisms may be used.

Returning now to FIG. 2, the restraint portion 24 includes a positioningmember 39. The positioning member 39 allows the user to adjust the burr18 up or down. By being able to adjust the vertical location of the burr18, the user can control the depth that the burr 18 will cut. Thevertically adjustable piece 39 includes a screw 40 that can be adjustedto different heights, allowing the burr 18 to be adjusted.

In another embodiment, the burr 18 may not be vertically adjustable.Instead, there may be provided a plurality of burrs that have differentdepths, which would allow for different heights to be cut.

FIGS. 4A and 4B show a top and a side view of the humerus 30. Asillustrated, the humerus 30 includes a greater humeral tubercle 44 (bestseen in FIG. 1) that needs to be either partially or wholly removed. Thegreater humeral tubercle 44 includes a radius R and a depth D. Thecutting guide 10 of the present invention will be able to cut both theradius R and the depth D in a single step, as will be described below.

Turning now to FIG. 5, a method for using the cutting guide 10 will bedescribed. First, at step s50, a humeral head 12 is resurfaced using aspherical reamer over the guide pin 28. The reamer allows for a flatsurface to be created on the top of the humeral head 12. At step s52,the length of the arm 20 is adjusted to the desired length. Next, atstep s54, the cutting guide 10 is placed over the guide pin 28. Thehousing 14 of the cutting guide 10 sits on the flat on the top of thehumeral head 12. The post 29 fits into the reamed hole. Next, at steps56, the cutting guide 10 is aligned using the pin holes 31 a, 31 b onthe housing 14. Pins 32 a, 32 b are placed in the pin holes 31 a, 31 bat step s56 to prevent rotation of the housing 14. At step s58, the arm20 and adjustable cylinder 22 are then placed over the guide pin 28 inthe parabolic slot 16 of the housing 20. The burr 18 is then placed intothe restraint portion 24 of the arm 20 at step s60. At step s62, thedepth of the burr 18 will be adjusted (if so desired). The arm 20 isthen rotated and translated along the parabolic slot 16 to resect theradius R and depth D simultaneously on the humerus 30 at step s64. Afterthe required part of the greater tubercle 42 is removed, the cuttingguide 10 is then removed from the guide pin 28 and the trialing andimplantation of the prosthesis can occur.

In some embodiments, step s52 may take place after the arm 20 is placedover the guide pin 28. In some embodiments, step 62 may not be included.In those embodiments, multiple burrs of different sizes may be includedand the surgeon selects one of the burrs depending on the depth thesurgeon would like to cut.

By placing the cutting guide 10 on the guide pin 28 that is used inother cutting procedures, reproducible and properly placed cuts can bemore easily achieved. Also, because of the three-dimensional parabolicnature of the slot 16, the radius and the depth can be cutsimultaneously, allowing for resection in multiple planes. Also, in someembodiments both the arm 20 and the burr are adjustable relative to thehousing 14, both the radius and the depth to be cut can be adjusteddepending upon the anatomy of the patient or the need of the surgeon.

Turning now to FIGS. 6 and 7, another embodiment of the presentinvention will be described. A cutting guide 100 is provided thatincludes an arm 102 that couples to the burr 18. The cutting guide 100further includes a housing 104. The housing 104 includes an opening 106to enable the housing 104 to slide over the guide pin 28. The cuttingguide 100 also includes a stem hole stabilizer 108 that attaches to thehousing 104 via a threaded portion 110 as shown in FIG. 6. The threadedportion 110 engages a threaded opening 112 in the housing 104. Thehousing 104 and stem hole stabilizer 108 can be adjusted verticallyrelative to the guide pin 28 via a screw 114 that locks the housing inposition on the guide pin 28.

In use, the arm 102 swings along a curved path on the humeral head 12,guiding the burr 18. The swinging of the arm 102 causes the burr 18 tocut off a radius of the greater tubercle. In other words, the burr 18swings along an arcuate path on the greater tubercle. In thisembodiment, another cutting guide would need to be used to cut theappropriate depth.

In one embodiment, the burr 18 is made of a stainless steel having ahardness between about 40 and 55 on the Rockwell scale. In embodimentswhere the burr 18 is only intended to be used once, the burr may be madeof a softer metal. In other embodiments, the burr 18 may be made of asofter metal, but may be coated with stainless steel having the hardnessdescribed above. The arm 20 may be made of stainless steel or othersterilizable metals. The arm 20 itself may also be a one-time instrumentmade of a polymer material. The housing 14 may also be made of stainlesssteel or other sterilizable metal. In other embodiments, the housing mayalso be made of a polymer material. In the above-described invention,the path cut was an arcuate path that included both a radius and adepth. In other embodiments, the multi-dimensional guide path could bedesigned so as to cut other dimensions that result in two planes beingsimultaneously cut. For example, in some embodiments, the path may be aparabolic slot that cuts both a radius and a width. In otherembodiments, the path may be of a different shape that cuts an oval or arectangle while simultaneously cutting another dimension.

Although the above-embodiments have been described being used with ahumeral head, it should be understood that the cutting guide of thepresent invention may be used to cut other bones in preparation ofarthroplasty.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made therein without departing from the spirit andscope of the present invention as defined by the appended claims.

We claim:
 1. A bone cutting assembly comprising: a guide pin having adistal tip that may be securely inserted into a bone to define a cuttingaxis; A housing having a cam surface and features which allow thehousing to be temporarily secured to the bone; A burr mounting arm whichcan be fitted on to the guide pin so that it can swing around thecutting axis and also translate up and down the guide pin; characterizedin that the burr mounting arm is configured to act against the camsurface as it is swung around the guide pin, so that the arm is causedto move up or down relative to the guide pin by the action of the camsurface; A burr cutting tool retained on the burr mounting arm, in whichthe burr cutting tool has an axis of rotation that is approximatelyparallel to the cutting axis defined by the guide pin; and A mountingcylinder that fits on to the guide pin and that includes a through boreextending transversely relative to the cutting axis, and in which theburr mounting arm can be received in the through bore, in which thespacing of one end of the burr mounting arm relative to the mountingcylinder can be adjusted.
 2. The bone cutting assembly of claim 1, inwhich the burr mounting arm is configured to act directly against thecam surface.
 3. The bone cutting assembly of claim 1, in which thehousing includes a slot defined by the cam surface and extendingtransverse to the cutting axis, and in which the burr mounting arm fitswithin the slot.
 4. The bone cutting assembly of claim 1, in which theburr mounting arm can be rotated about the cutting axis through an angleof at least 10°.
 5. The bone cutting assembly of claim 1, in which theburr mounting arm can be rotated about the cutting axis through an angleof not more than about 180°.
 6. The bone cutting assembly of claim 1, inwhich the cam surface, when viewed in the direction of the cutting axis,is shaped like a portion of a circle.
 7. The bone cutting assembly ofclaim 1, in which the cam surface has a generally concave profile whenviewed in a direction transverse to the cutting axis.